3 



AMMONITES dentatus. 

 TAB. CCCVIII. 



Spec. Char. Discoid, iimbilicate, radiated ; front 

 square* ; radii prominent and forked near 

 their commencement^, terminating upon tlie 

 edffes of the front. 



Syn. Am. scrratus. Parkinson in Trans, GeoL 



Soc. V. 57. 



Although this shell may be described as umbilicated, 

 the inner whorls are in part exposed : the radii are 

 ^lightly curved ; they are most prominent at a short 

 distance from their commencement, where also they are 

 forked ; each branch is slightly enlarged and bent 

 forward upon the edge of the front, where it ends : thus 

 the front has two serrated edges, the intermediate space 

 being plain : the aperture occupies about two-fifths of 

 the diameter of tlie (Shell in length, and is one-fourtli 

 in width. 



This appears to be A. serratus of Parkinson ; but as 

 it is totally different from the Ammonite, to which that 

 name had been previously given at tab. 24 of this work, 

 it has become necessary to change it. 



AMMONITES laiitus. 



Spec. Char. Discoid, radiated ; inner whorls half 

 concealed ; front narrow, slightly concave ; 

 principal radii slender, varicose, or tubercu- 

 lated near their commencement ; shorter radii 

 alternating, united in pairs to form compressed 

 tubercles upon the edges of the front. 

 SvN. Am. lautus. Parkinson in Trans. GeoL 

 Soc. r. 58. 



var. a, radii long, elegantly arched, and regular. 



var. /3, radii short, irregular, with strong tuber- 

 cles near their commencement. 



A HE inner whorls are more exposed in this than in the 

 Sast, and the sides of the whorls generally more convex, 

 especially in a : in var. /3 the lesser radii are often joined 

 at the tubercles to the larger ones ; the form of the 

 aperture approaches to elliptical. 



Figures 1 and 2 are from var. a, and fig. 6 var. & ; 



* The siphuiicle ii nofa^timej decomposed away, and leaves a hollow 

 ^at may deceive<. 



